1. Field of the Invention
This invention relates generally to laser assemblies, and more particularly to a method of converting an optical wavelength using a widely tunable laser assembly with an integrated modulator.
2. Brief Description of the Related Art
A laser transmitter for fiber optic networks must provide signals at a given stable wavelength, modulated at a desired rate with low chirp and an appropriate power launched into optical fiber. Current networks have as many as 100 wavelength channels with one laser devoted to each channel, and each laser having an external modulator. Significantly greater efficiencies could be realized with a laser transmitter and a modulator included on a chip, wherein the modulated laser is capable of being tuned to cover every channel of a system. Photonic integration can be used to provide a laser transmitter on a chip, as is well understood in the art. FIG. 1 shows a block diagram of a structure that can be used to accomplish this. While photonic integration is well known in the art, prior art efforts have been focused on the integration of lasers that are not widely tunable . Kobayashi, N.; Noda, A.; Watanabe, T.; Miura, S.; Odagawa, T.; Ogita, S. xe2x80x9c2.5-Gb/s-1200-km transmission of electroabsorption modulator integrated DFB laser with quarter-wavelength-shifted corrugation,xe2x80x9d IEEE Photonics Technology Letters, vol. 11, (no. 8), IEEE, August 1999. p. 1039-41; Delprat, D.; Ramdane, A.; Silvestre, L.; Ougazzaden, A.; Delorme, F.; Slempkes, S. xe2x80x9c20-Gb/s integrated DBR laser-EA modulator by selective area growth for 1.55- mu m WDM applications,xe2x80x9d IEEE Photonics Technology Letters, vol. 9, no. 7, IEEE, July 1997. p. 898-900. Large tuning ranges make achieving adequate performance of these functional blocks non-obvious with respect to the teachings of the prior art in general, and the prior art related to narrowly tunable devices in particular. What is needed is photonic integration techniques to construct a widely tunable laser apparatus including an integrated modulator.
Accordingly, an object of the present invention is to provide a method of modulating an optical wavelength using a laser assembly where all of the elements are fabricated on a single wafer.
Another object of the present invention is to provide a method of modulating an optical wavelength using a diode laser assembly with the elements derived from a common epitaxial layer structure.
A further object of the present invention is to provide a method of modulating an optical wavelength using a widely tunable diode laser assembly with an integrated modulator.
Yet another object of the present invention is to provide a method of modulating an optical wavelength using a diode laser assembly with the elements fabricated on a single wafer by common process steps.
A further object of the present invention is to provide a method of modulating an optical wavelength using a monolithically integrated diode laser assembly made with fabrication steps that tailor optical properties of selected regions to a desired electro-optic function.
Another object of the present invention is to provide a method of making a monolithically integrated diode laser assembly that uses common fabrication process steps to form the elements of the assembly that are compatible with photonic device fabrication processes presently used in the lightwave industry.
These and other objects of the present invention are achieved in a method of converting an optical wavelength that provides a wavelength converter assembly with a photodetector and a laser with a common epitaxial structure. The expitaxial structure has areas of differing bandgap. An optical input having a first wavelength at the wavelength converter assembly is absorbed. A first electrical signal is generated from the photodetector in response to the optical input. The first electrical signal is conditioned to produce a conditioned first electrical signal. A second electrical signal is generated from the conditioned first electrical signal. A laser output is generated from a gain medium of the laser at a second wavelength in response to the second electrical signal.
In another embodiment of the present invention, a method of converting an optical wavelength provides a wavelength converter assembly having an epitaxial structure with areas of differing bandgap. A waveguide layer is positioned between first and second semiconductor layers of the epitaxial structure. An optically active gain medium is positioned between first and second reflectors that define a resonant cavity. The wavelength converter assembly also includes a photodetector. An optical input is detected at the photodetector. A laser output is generated from the wavelength converter assembly in, response to the optical input.